Highly aligned thin film tape head and method of making same

ABSTRACT

Reducing alignment errors between a read element and corresponding write elements permits narrower data tracks and, hence, greater data density on magnetic tape. A method for manufacturing a thin film tape head having multiple write elements and at least one read element corresponding to each write element is provided. Excess material is trimmed from each write element to align the write element with corresponding read elements. The excess material may be track trimmed using a focused ion beam.

TECHNICAL FIELD

The present invention relates to thin film magnetic tape recording headsfor accessing magnetic tape possessing a high degree of alignmentbetween read elements and write elements accessing a particular datatrack.

BACKGROUND ART

Reliability, cost-efficiency, and ease of use make magnetic tape themedium of choice for many information storage and retrievalapplications. Typically, multiple data tracks are written simultaneouslyby write elements in a tape head. Similarly, multiple read elements areused to simultaneously sense multiple data tracks. The desire toincrease information density held by magnetic tape has resulted innarrower and more closely spaced data tracks. This results in the needfor close alignment between head elements which access each data track.This is particularly true for read-after-write operations in which datais read immediately following the write operation to verify thecorrectness of recorded data.

A tape head generally contains multiple write elements to simultaneouslywrite multiple tracks for achieving a high rate of data transfer.Multiple read elements are used to achieve the same rate of datatransfer during play back operations. The tape head is constructed usingthin film techniques to permit the small element geometry required forhigh information density recording and to reduce the cost of productionby applying replication and manufacturing techniques similar to thoseused in integrated circuit production. Many tape head designs arepossible. One design consists of separate read modules and writemodules. Each write module includes multiple write elements spacedacross the tape surface. Similarly, each read module consists ofmultiple read elements spaced across the tape surface. The tape head isconstructed by attaching read and write modules. A typical constructionhas one write module sandwiched between two read modules to permitread-after-write operation in either tape direction. Tape heads of thisdesign are described in U.S. patent applications Ser. No. 08/939,773titled “Magnetic Tape Head Assembly” filed Sep. 29, 1997 by R. Dee etal. and Ser. No. 08/975,645 titled “Magnetic Tape Head Assembly HavingSegmented Heads” filed Nov. 21, 1997 by R. Dee et al., both of which areincorporated by reference herein. Another design has pairs of readelements and write elements constructed in the same module. At least twomodules are joined together to permit read-after-write tape operation ineither direction. Designs of this type are described in U.S. Pat. No.5,264,981 titled “Multilayered Ferromagnetic Film And Magnetic HeadEmploying Same,” U.S. Pat. No. 5,208,714 titled “Magnetic HybridInterleaved Head With Closure Supporting Islands,” and U.S. Pat. No.5,142,768 titled “Method For Making Magnetic Head With EnhancedPoletip,” each of which are incorporated by reference herein.

In designs having read and write elements in the same module, alignmenterrors between paired read and write elements may be compensated bychanging the azimuth angle. The azimuth angle is defined as the anglebetween a line running along the center of the data track and a linethrough the center of corresponding read and write elements. One problemwith this technique in multiple module tape heads is that changing theazimuth angle to improve element alignment within one module may worsenelement alignment in another module. Another difficulty is thatincreasing the azimuth angle introduces a skew distance in the tapedirection between write elements and between read elements. The skewdistance causes the same point along the length of a data track in eachdata track across the width of the tape to cross write elements or readelements at a different time. This skew time requires the introductionof skew buffers to ensure proper writing and reading of data. Skewcompensation buffers are expensive and require complicated logic.

Alignment problems may be even greater in tape heads constructed withseparate read and write modules. Since it is unlikely that a line can bedrawn through the center of all elements accessing a given data track,changing the azimuth angle will not correct for alignment problems intape heads having separate read and write modules.

What is needed is a system and method for highly aligned elements withina magnetic tape head. The tape head should be economical to produce andshould be constructed by readily available manufacturing processes.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide for improved tapehead element alignment.

Another object of the present invention is to provide for decreased skewdistances in read-write modules.

Still another object of the present invention is to provide fordecreased element alignment errors in multiple module tape heads.

Yet another object of the present invention is to provide a tape headhaving closely aligned read and write elements that are constructedusing readily available manufacturing processes.

A further object of the present invention is to provide a tape headhaving closely aligned read and write elements that is economical toproduce.

In carrying out the above objects and other objects and features of thepresent invention, a method for manufacturing a thin film tape headhaving multiple write elements and at least one read elementcorresponding to each write element is provided. Alignment is achievedby trimming excess material from each write element to align the writeelement with the at least one corresponding read element. This trimmingmay be accomplished using a focused ion beam.

A thin film read-write-read tape head is provided. The tape headincludes a write module having write elements. Each write element has atop pole and a bottom pole for writing a data track, the data trackwidth defined by the lengths of the top pole and the bottom pole. Thetape head also includes one read module on either side of the writemodule. Each read module has a read element corresponding to each writeelement for reading the data track. The poles are trimmed to removeexcess pole material outside of a desired data track width centeredacross a line between corresponding read elements in each read module.

A method for manufacturing a thin film tape head includes constructingat least one write module having multiple write elements. Each writeelement includes top and bottom poles constructed with excess materialin a direction defining data track width. The write module is assembledbetween two read modules. Each read module has a read elementcorresponding to each write element. Excess material to be removed fromthe top pole and the bottom pole of each write element is determinedsuch that material remaining forms a write element having a desiredtrack width aligned between the corresponding read elements. The excessmaterial is then trimmed from the top pole and the bottom pole of eachwrite element.

In an embodiment of the present invention, determining the excessmaterial to remove includes measuring the location of the center foreach of the two read elements corresponding to a write element. Anazimuth line from the first read element center through the second readelement center is determined. The intersection of the write elementcenter along the azimuth line is determined. The excess material is thatportion of the top pole and the bottom pole outside of a region defininga desired data track width centered on the intersection. The tape headmay then be mounted such that the azimuth line is parallel with eithertape direction.

A thin film read-write module is also provided. The read-write moduleincludes write elements aligned along a gap line. Each write element hastop and bottom poles for writing a data track. The data track width isdefined by pole lengths. The module also includes a read elementcorresponding to each write element for reading the data track. The topand bottom pole lengths are trimmed to remove excess pole materialoutside of a desired data track width centered across a line through thecorresponding read element center and normal to the gap line.

A method of manufacturing a read-write module is provided. Theread-write module includes write elements aligned along a gap line and aread module corresponding to each write element. The center of a readelement is located. An azimuth line normal to the gap line and throughthe center of the read element is determined. Excess material from thewrite element top and bottom poles is trimmed such that a desired datatrack width is centered on the azimuth line.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptualized drawing of a prior art read-write-read tapehead;

FIG. 2 is a conceptualized drawing illustrating misalignment betweenelements in a read-write-read tape head;

FIG. 3 is a conceptualized sectional view of a read module and a writemodule showing element construction;

FIG. 4 is a conceptualized view of track trimming a write element in aread-write-read tape head according to an embodiment of the presentinvention;

FIG. 5 is a conceptualized view of a read-write-read head according toan embodiment of the present invention;

FIG. 6 is a conceptualized view of a prior art read-write module; and

FIG. 7 is a conceptualized view of track trimming a write element in aread-write module according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, a conceptualized drawing of a prior artread-write-read tape head is shown. Tape head 20 accesses magnetic tape22 passing by tape head 20 in tape direction 24. Tape head 20 includeswrite module 26 sandwiched between first read module 28 and second readmodule 30. Write module 26 includes multiple write elements 32, eachoperative to write data track 34 on magnetic tape 22. Each read module28,30 includes one read element 36 corresponding to each write element32 in write module 26. Each read element 36 can read data from datatrack 34 on magnetic tape 22.

Typically, at least one read module 28,30 includes servo read elements38 for reading servo tracks 40 recorded on magnetic tape 22. Patternsrecorded on servo track 40 permit tape head 20 to be moved in adirection substantially normal to tape direction 24 to position elements32,36 over data track 34. For example, data track 34 may be positionedso that data track center 42 is centered over write element 32 during awrite operation.

Write module 26 may include fiducial marks 44 aligned with writeelements 32. Fiducial marks 44 permit tape head 20 to be mounted suchthat the alignment of write elements 32 is normal to the path ofmagnetic tape 22 moving by tape head 20.

Modules 26,28,30 are manufactured using thin film techniques that permitthe spacing between elements 32,36 within a module to be accuratelymaintained. Modules 26,28,30 are then bonded together to form tape head20. This bonding process is not as accurate as thin film manufacturing,resulting in misalignment between write element 32 and correspondingread elements 36 which access the same data track 34. This misalignmentis particularly troublesome during read-after-write operations whencentering write element 32 on data track 42 may result in the center ofread element 36 being positioned away from data track center 42 in adirection normal to data track center 42.

Referring now to FIG. 2, a conceptualized drawing illustratingmisalignment between elements in a read-write-read tape head is shown.Write element 32 includes top hole 50 and bottom pole 52 separated bygap 54. Magnetic flux flowing in gap 54 between top pole 50 and bottompole 52 produces field patterns on data track 34. The width of datatrack 34, indicated by 56, is determined by the length of poles 50,52 ina direction normal to data track center 42. Gap line 58 runs through thecenter of gap 54 for each write element 32 in write module 26.

Misalignment distance 60 may be defined as the distance between thecenter of read element 36 and data track center 42 in a direction normalto data track center 42 when data track 34 is centered over writeelement 32. Previous manufacturing methods produce read head 20 withmisalignment distance 60 within ±4 microns within three standarddeviations. This is not sufficient for higher density magnetic tape 22which may have data track widths 56 of twenty microns or less.

Referring now to FIG. 3, a conceptualized sectional view of a readmodule and a write module illustrating element construction is shown.The proportions shown for write element 32 and read element 36 are notaccurate and the spacing between elements 32,36 is much greater thanactually shown.

An electromagnet is formed by bottom pole 52, top pole 50, and aconductive coil shown generally by 70, in write element 32. A current incoil 70 induces flux in poles 50,52. This flux produces a field at gap54. As tape 22 moves across tape contact surface 72 in tape direction24, the field produced by current in coil 70 produces magnetizationfields on tape 22, not shown for clarity.

Poles 50,52 are typically constructed of a magnetically permeable alloyor amorphous mixture including at least one of elements cobalt, nickel,and iron. Coil 70 is a conductor, such as copper, that is insulated frompoles 50,52 by insulation layer 74. Insulation layer 74 may be builtfrom layers of photoresist with a layer of alumina against one of poles50,52, the alumina extending into gap 54. Write element 32 may be builton substrate 76 and capped with cover layer 78, both of which may beconstructed of an insulator with good wear properties such as AlTiC.

Read element 36 typically includes a magnetoresistive sensor, showngenerally by 80, which exhibits a change in resistance due tomagnetization fields on magnetic tape 22 moving over tape contactsurface 72 in tape direction 24. Magnetoresistive sensor 80 is built onsubstrate 82 and includes cover layer 84. Substrate 82 and cover layer84 are typically made of a magnetically permeable material, such asnickel-zinc (NiZn) ferrite, to enhance the sensitivity ofmagnetoresistive sensor 80.

Feed through between write element 32 and read element 36 may be reducedby including shield 86 typically constructed of a conducting materialsuch as brass. Write module 26 and read module 28,30 constructed in thismanner are typically bonded together using cyanoacrylate or an epoxy.

The previous discussion describes a typical tape head 20 forillustrative purposes and is not meant to limit the present invention totape head 20 having only this construction. As will be recognized by oneof ordinary skill in the art, a wide variety of tape heads 20 may beconstructed within the spirit and scope of the present invention. Forexample, various other materials, geometries, and orientations may beused for write element 32. Similarly, read element 36 may bemagnetoresistive, inductive, or the like.

Referring now to FIG. 4, a conceptualized view of track trimming a writeelement in a read-write-read tape head according to an embodiment of thepresent invention is shown. Write element 32 is constructed with toppole 50 and bottom pole 52 having excess material in a directiondefining data track width 56, as indicated by pole length 90. Tape head20 is assembled with write module 26 between first read module 28 andsecond read module 30. First read module 28 includes a first readelement corresponding to write element 32, shown generally by 92. Secondread module 30 includes a second read element corresponding to writeelement 32, indicated generally by 94. Material is trimmed from top pole50 and bottom pole 52 such that desired data track width 56 is centeredacross azimuth line 96 extending between first corresponding readelement 92 and second corresponding read element 94.

The amount of excess material to remove from top pole 50 and bottom pole52, shown generally by 98, may be determined by first measuring thelocation of first corresponding read element 92 and second correspondingread element 94. This may be accomplished using a measuring microscopeunder computer control such as is available from Pacific PrecisionLaboratories of California. The measuring microscope can determineazimuth line 96 through the center of first corresponding read element92 and second corresponding read element 94. The measuring microscopenext determines the intersection of azimuth line 96 with the center ofwrite element 32.

In an embodiment of the present invention, the intersection of azimuthline 96 and gap line 58 produces the center of write element 32. Theintersection of gap line 58 with azimuth line 96 is defined to beintersection point 100. Azimuth angle 102 is defined as the anglebetween azimuth line 96 and gap line normal 104. Gap line normal 104 isa line normal to gap line 58 through intersection point 100. Excessmaterial 98 is determined to be that portion of top pole 50 and bottompole 52 outside of a region defining track width 56 centered on theintersection of gap line 58 and azimuth line 96. Data track width 56 mayextend in a direction parallel with gap line 58 as shown or may extendin a direction normal to azimuth line 96.

Excess material 98 is preferably removed by track trimming write element32 with a focused ion beam. The focused ion beam produces etch pattern106 removing excess material 98 from top pole 50 and bottom pole 52 to adepth of approximately one micron. The focused ion beam used operatedwith a 15 nanoampere beam current and a beam energy of 50 keV. Thefocused ion beam may be produced by a focused ion beam workstation suchas is available from the FEI Company of Hillsburo, Oreg.

Referring now to FIG. 5, a conceptualized view of a read-write-read headaccording to an embodiment of the present invention is shown. Tape head20 is mounted so that azimuth line 96 is parallel with tape direction24. This may be accomplished by establishing gap line 58 through twofiducial marks 44, one of which is shown in FIG. 5. Tape head 20 is thenrotated such that gap line 58 forms azimuth angle 102 with a normal totape direction 24.

Referring now to FIG. 6, a conceptualized view of a prior art read-writemodule is shown. Read-write module 120 includes both write elements 32and read elements 36. Due to manufacturing inaccuracies, the particularread element corresponding to write element 32, shown generally by 122,may not be centered on gap line normal 124 which is perpendicular to gapline 58 and intersects the center of write element 32. Azimuth angle 126is defined as the angle between center line 128 running through thecenters of write element 32 and corresponding read element 122 and gapline normal 124. Rotating read-write module 120 by azimuth angle 126places center line 128 parallel with tape direction 24. This permits thecenters of write element 32 and corresponding read element 122 to bealigned with data track center 42 for data track 34 on magnetic tape 22.

While this approach greatly reduces alignment errors between writeelement 32 and corresponding read element 122, rotating read-writemodule 120 introduces skew distance 130 between write elements 32 andbetween read elements 36. Skew distance 130 causes each write element 32or read element 36 to cross an arbitrary line normal to track center 42across the width of tape 22, shown generally by 132, at different times.Skew buffers are required to synchronize data written to or read frommagnetic tape 22. These skew buffers add complexity and cost to a tapesystem including read-write module 120.

Referring now to FIG. 7, a conceptualized view of track trimming a writeelement in a read-write module according to an embodiment of the presentinvention is shown. The need for skew buffers can be eliminated if writeelements 32 are track trimmed so that no rotation of read-write module120 is necessary to align the center of a write element 32 andcorresponding read element 122 with data track center 42. Read-writemodule 120 is constructed with top pole 50 and bottom pole 52 havingpole length 90 considerably longer than the desired data track width 56.Using techniques similar to those described with regards to FIG. 4above, the center of corresponding read element 122 is located. Azimuthline 140 is found normal to gap line 58 through the center ofcorresponding read element 122. Intersection point 142 is found whereazimuth line 140 crosses gap line 58. Excess material, indicatedgenerally by 98, is trimmed from top pole 50 and bottom pole 52 suchthat the desired data track width 56 is centered on azimuth line 140 ina direction parallel to gap line 58. Excess material 98 is preferablyremoved from top pole 50 and bottom pole 52 with a focused ion beamforming etched patterns 106.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, it is intended that thefollowing claims cover all modifications and alternative designs, andall equivalence that fall within the spirit and scope of this invention.

What is claimed is:
 1. A method for manufacturing a thin film tape headhaving a plurality of write elements and a plurality of read elements,two read elements corresponding to each write element, wherein excessmaterial is trimmed from each write element to align the write elementwith the corresponding read elements, the trimmed material based on anazimuth line extending between the corresponding read elements so as todetermine a write track based on the relative positions of thecorresponding read elements.
 2. A method for manufacturing a thin filmtape head as in claim 1 wherein excess material is trimmed using afocused ion beam.
 3. A method for manufacturing a thin film tape head asin claim 1 further comprising mounting the tape head so that the azimuthline is parallel with a direction of tape travel over the tape head. 4.A method for manufacturing a thin film tape head for accessing datatracks on magnetic tape passing the tape head in a tape directioncomprising: constructing at least one write module having a plurality ofwrite elements, each write element including a top pole and a bottompole, each pole constructed with excess material in a direction definingdata track width; assembling the write module between two read modules,each read module having a read element corresponding to each writeelement thereby permitting read-after-write in either tape direction;for each write element, measuring the location of a first correspondingread element center; measuring the location of a second correspondingread element center; determining an azimuth line from the firstcorresponding read element center through the second corresponding readelement center; determining the intersection of the write element centeralong the azimuth line; determining as excess material that portion ofthe write element top pole and the write element bottom pole outside thedesired track width centered on the determined intersection; andtrimming the determined excess material from the top pole and bottompole.
 5. A method for manufacturing a thin film tape head as in claim 4further comprising mounting the tape head so that the azimuth line isparallel with the tape direction.
 6. A method for manufacturing a thinfilm tape head as in claim 4 wherein trimming the determined excessmaterial comprises track trimming each write element with a focused ionbeam.
 7. A method of manufacturing a read-write module, the read-writemodule having a plurality of write elements aligned along a gap line anda read element corresponding to each write element, each write elementhaving a top pole and a bottom pole, the length of the top pole andbottom pole defining a data track width, the method comprising: locatingthe center of at least one read element; for each located read elementcenter, determining an azimuth line normal to the gap line and throughthe located read element center; and trimming excess material from thetop pole length and the bottom pole length such that a desired datatrack width is centered on the azimuth line.
 8. A method ofmanufacturing a read-write module as in claim 7 wherein trimming excessmaterial comprises removing portions of the top pole length and thebottom pole length with a focused ion beam.
 9. A method of manufacturinga read-write module as in claim 7 further comprising mounting theread-write module so that the azimuth line is parallel with a directionof tape travel over the tape head.